Novel method for preparing purified extracts of harpagophytum procumbens

ABSTRACT

A method for preparing a concentrated extract of  Harpagophytum procumbens , in liquid or dry form, having a harpagoside titre greater than or equal to 5%, comprises a step of purifying a crude extract of  Harpagophytum procumbens  in liquid form in aqueous phase by a technique of liquid-liquid extraction with an organic solvent selected from the esters.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. National Stage patentapplication Ser. No. 12/599,146, filed on Aug. 20, 2010.

The present invention relates to a method for preparing purifiedextracts of Harpagophytum procumbens, said extracts being in liquid ordry form.

The present invention relates also to purified extracts as obtained bysaid method. Harpagophytum (Harpagophytum procumbens) is a plant nativeto South Africa which is traditionally known for its efficacy in thetreatment, inter alia, of arthrosis pain.

Its tuberous lateral roots contain in particular compounds of theiridoid type, glycosylated or unglycosylated, which are considered to bethe active ingredients and are called harpagoside, harpagide, procumbideand procumboside.

Modern phytotherapy uses plant powder or plant extracts in galenicalformulations in dry form of the gelatin capsule type. The use of plantpowder means that a very large number of doses must be taken per day,which is very restricting on a daily basis.

The food supplement and phytotherapy industries now have available alarge number of plant extracts for these applications.

Harpagophytum extracts are usually obtained using aqueous alcoholicsolvents, it being possible for the alcohol titre to vary from 0(extract with water) to 90% (Chrubasik S.; Devil's claw extract as anexample of the effectiveness of herbal analgesics; Orthopade. 2004 July;33(7): 804-808).

The European Pharmacopoeia also describes, in the monograph of theHarpagophytum root, the use of methanol for the extraction ofharpagoside.

The plant is separated from the extraction solvent by any conventionalprocess, for example of the filtration or centrifugation type. Where analcoholic solvent is used, the solvent is removed from the filtrate, andthe filtrate is optionally concentrated in order to reduce the volumeand then dried.

This type of process makes it possible to obtain harpagophytum extractshaving a harpagoside titre of approximately from 2.5 to 3%, measured byHPLC. In addition, variation of the usual parameters of the vegetalextraction, such as the nature of the solvent, the temperature andduration of the extraction, has no effect on the final titre of theresulting powder. A titre of about 2.5 to 3% is always obtained.

Products having a harpagoside titre of from 2.5 to 3% by HPLC offer asatisfactory alternative to the use of plant powder to produce gelatincapsules but do not enable the dosage to be reduced significantly forthe treatments for which harpagophytum is effective.

Only products having a higher harpagoside titre would be able to limitthe daily dose of gelatin capsules significantly.

Therefore, there is a lack of a method which allows powderedharpagophytum extracts to be obtained industrially with high harpagosidetitres.

Among the means described for obtaining such a result, and even though,given the polarity of the molecule, the person skilled in the art is notimmediately drawn to this solution, mention may be made of the use ofsuper- or sub-critical fluid (Gunther M, Laufer S, Schmidt PC. Highanti-inflammatory activity of harpagoside-enriched extracts obtainedfrom solvent-modified super- and subcritical carbon dioxide extractionsof the roots of Harpagophytum procumbens; Phytochem Anal. 2006,January-February; 17(1): 1-7).

Extractions of Harpagophytum procumbens roots with carbondioxide/solvent modified have been studied in respect of the extractionefficiency and the harpagoside content and have been compared with aconventional extract.

The effects of the pressure, the temperature and the type andconcentration of the modifying agent were examined. Two extraction stepswere necessary to obtain anti-inflammatory extracts that were greatlyenriched with harpagoside. The first extraction step was carried out inthe supercritical state using carbon dioxide modified with n-propanol toremove the undesirable lipophilic substances. The main extraction wascarried out in the supercritical or subcritical state with carbondioxide modified with ethanol. The supercritical liquid extractionyielded extracts containing up to more than 30% harpagoside. Thesubcritical extracts exhibited a harpagoside content of 20%, but theextraction yield was almost three times greater than under supercriticalconditions.

The level of recovery of harpagoside, given by the sum of the extractand the crude residue, was 99% greater than in all the precedingexperiments. The conventional extract and two carbon dioxide extractswere examined for the in vitro inhibition of 5-lipoxygenase, or2-cyclooxygenase biosynthesis. The two carbon dioxide extracts exhibitedtotal inhibition of the biosynthesis of 5-lipoxygenase at aconcentration of 51.8 mg/l; in contrast, the conventional extract doesnot exhibit inhibition of 5-lipoxygenase biosynthesis.

The value of purified extracts of harpagophytum root is dearlydemonstrated here. However, it is necessary to replace this type ofsuper- or sub-critical CO₂ extract in an industrial context. Theextracts obtained by means of CO₂ are in a very high price range, muchhigher than extracts by means of solvent, and this type of processrequires very large installations, given the very high pressures thatare employed.

The products obtained by CO₂ extraction are not generally in powder formbut rather in the form of a paste or wax, which is not compatible withthe production of gelatin capsules, for example, or may be adsorbed on asupport, which reduces the titre of the product. In addition, theproducts so obtained are liposoluble extracts and are thereforeinsoluble in aqueous phases. Finally, it is pointed out that this typeof process using CO₂ results in compounds of the pesticide and mycotoxintype, and therefore concentrates them in the finished product.Accordingly, CO₂ extractions do not permit the preparation ofharpagophytum extracts having a high harpagoside titre that arecompatible with all liquid or dry galenical formulations.

Accordingly, it is an object of the present invention to provide anindustrially applicable method for preparing purified extracts ofharpagophytum having a high harpagoside titre, said extracts so obtainedbeing compatible with all liquid (syrups or capsules) or dry (tablets orgelatin capsules) galenical formulations.

It is also an object of the present invention to provide harpagophytumextracts which have a high harpagoside titre and are soluble in aqueousphases.

The present invention relates to a method for preparing a concentratedextract of Harpagophytum procumbens, in liquid or dry form, having aharpagoside titre greater than or equal to 5%, preferably greater thanor equal to 35%, which method comprises a step of purifying a crudeextract of Harpagophytum procumbens in liquid form in an aqueous phaseusing a technique of liquid-liquid extraction with an organic solventselected from the esters, especially the aliphatic esters, and moreparticularly from the alkyl acetates, said alkyl group being a branchedor linear alkyl chain having from 1 to 10, especially from 1 to 6 andpreferably from 1 to 4 carbon atoms.

Accordingly, the present invention is based on the fact that theinventors have found that iridoid glucosides of harpagophytum can,surprisingly, be purified by means of solvents of the ester type.

The use of solvents such as alcohols and ketones is known at present.

Although the Snyder polarity ranks ethyl acetate (4.1) on the same levelas ethanol (4.3) but lower than methanol (5.1) and acetone (5.1) andslightly higher than butanol (3.9), the dielectric constant of ethylacetate (ε=6) is extremely low and does not suggest at all that ethylacetate may create affinity bonds with polar molecules, thussolubilizing them and a fortiori purifying molecules of the iridoidglucoside type.

Surprisingly, esters such as ethyl acetate are very selective in respectof this type of compound and permit very efficient purifications totitres greater than 35% on a dry basis.

Among all the pitfalls encountered during the production of aharpagophytum extract, there is the difficulty associated withdegradation of the active ingredients. Accordingly, the person skilledin the art uses solvents such as water or alcohols to prepare the crudeextracts, and solvents such as alcohols and aliphatic ketones to purifythem.

If such extracts are prepared under conventional conditions (extraction,removal of the organic solvent in vacuo if necessary, concentration toobtain a crude extract, which can be dried or purified by means of adifferent organic solvent, followed by removal of the organic solvent invacuo, concentration and drying), harpagoside titres below 3% are alwaysobtained. The intermediate products are much more concentrated, but thedifferent steps lead to gradual degradation of the active ingredients.

Among the improvements that have been proposed there may be mentioneddrying in an organic solvent phase (alcohol or butanol) (as described,for example, in U.S. Pat. No. 6,280,737), which requires equipment thatis very expensive and does not perform very well. In all cases, theharpagoside titres of the extracts so obtained are 20% at the maximum.

The use of a water-immiscible organic solvent of the butanol type forthe purification of harpagophytum extracts also presents the problem ofthe temperature imposed on the product in order to remove said organicsolvent. Butanol on its own boils at 117° C. at ambient temperature, andthe water/butanol mixture encountered during the purification stepsboils at 92.6° C. Even under conditions of evaporation—drying in vacuo,the product is exposed to a high temperature, which leads to degradationof the active ingredients.

The use of a water-immiscible solvent of the ester type allows theoperations of evaporation—drying to be carried out at a much lowertemperature and therefore enables degradation of the active ingredientsto be limited. Accordingly, the use of esters having a boiling pointbelow that of the alcohols used in the prior art (especially butanol)allows the product (active ingredient—harpagoside) not to be exposed tohigh temperatures, which allows the duration of the process exposing theproduct to high temperatures to be reduced. Thermal degradation of theactive ingredient does not take place, and high titres of the resultingpurified extracts can be retained (up to at least 35%).

In addition, because the product can be concentrated at low temperature,it is possible to prepare a concentrate in aqueous phase that is devoidof the organic solvent fraction and make a gain in productivity in thedrying step, which can be carried out on equipment that is standard andtherefore less expensive and therefore of better dimensions.Lyophilization can be a drying means that is used, for example.

The harpagoside titre mentioned above is a weight/weight (w/w) titreexpressed based on the total weight of dry matter.

It is measured by the method of the European pharmacopoeia 5.07, asfollows: the procedure used is liquid chromatography using methylcinnamate as internal standard.

Preparation of the Internal Standard Solution:

0.130 g of methyl cinnamate is dissolved in 50 ml of methanol and madeup to 100.0 ml with the same solvent.

Preparation of the Solution to be Analyzed:

50 ml of methanol are added to 0.500 g of powdered harpagophytum(Harpagophytum procumbens) root. Stirring is carried out for 1 hour,followed by filtration. The residue is then transferred to a 100 mlflask, 50 ml of methanol are added, and the mixture is heated at refluxfor 1 hour. The whole is then cooled and filtered. The flask and thefilter are then washed with 2×5 ml of methanol. The extracts are thencombined and evaporated to dryness under reduced pressure and at atemperature not exceeding 40° C. The residue is then treated with 3×5 mlof methanol, and the extracts are filtered in a 25 ml volumetric flask.The filter is washed, and the mixture is made up to 25.0 ml withmethanol. 1.0 ml of internal standard solution is added to 10.0 ml ofthat solution, and the mixture is made up to 25.0 ml with methanol.

Preparation of the control solution: 0.5 ml of control solution (1 mg ofharpagoside in 1 ml of methanol) are removed and made up to 2.0 ml withmethanol.

Chromatography can be carried out, for example, using:

-   -   a stainless steel column having a length of 0.10 m and an inside        diameter of 4 mm, filled with octadecylsilylated silica gel for        chromatography (5 μm),    -   as mobile phase, at a flow rate of 1.5 ml/minute, a mixture of        equal volumes of water and methanol,    -   as detector, a spectrophotometer set at 278 nm,    -   and a 10 μl loop injector.

Analysis by Chromatography:

the solution to be examined is injected and the sensitivity of thesystem is adjusted so that the height of the peak corresponding tomethyl cinnamate represents 50% of the total scale of the recorder.

The harpagoside retention time is determined using 10 μl of controlsolution examined under the same conditions as the solution to beexamined. The harpagoside content (%) is then calculated using theexpression:

$\frac{m_{2} \times F_{1} \times 7\text{,}622}{F_{2} \times m_{1}}$

where m₁=mass of the test portion (g)

-   -   m₂=mass of the methyl cinnamate (g) in the internal reference        solution    -   F₁=area of the peak corresponding to harpagoside in the        chromatogram obtained with the solution to be analyzed    -   F=area of the peak corresponding to methyl cinnamate in the        chromatogram obtained with the solution to be analyzed.

According to a particular embodiment, the present invention relates to amethod for preparing a concentrated extract of Harpagophytum procumbens,in liquid or dry form, having a harpagoside titre greater than or equalto 5%, which method comprises the following steps:

-   -   a purification step of the type liquid-liquid extraction between        a crude extract of Harpagophytum procumbens in liquid form in        aqueous phase and an organic solvent selected from the esters,        in order to obtain an aqueous phase and a        harpagoside-concentrated organic phase,    -   a step of removal of the solvent from the organic phase obtained        previously, in order to obtain said concentrated extract in        liquid form, and    -   an optional step of conversion of said concentrated extract in        liquid form by physical or physico-chemical means in order to        obtain a concentrated extract in dry form.

The harpagoside-concentrated organic phase preferably has a harpagosidetitre greater than or equal to 5%.

According to an advantageous embodiment of the present invention, theorganic solvent used in the purification step by a technique of theliquid-liquid extraction type is selected from the esters, especiallythe aliphatic esters, and more particularly from the C₁-C₆—, preferablyC₁-C₄-alkyl acetates.

The organic solvent used for the liquid-liquid extraction step ispreferably methyl acetate, ethyl acetate or butyl acetate.

Ethyl acetate is particularly preferred because it is the most common onan industrial scale, has a very low boiling point (77.06° C.) and is analimentary solvent. Accordingly, ethyl acetate has the advantage ofbeing a water-immiscible solvent which is permitted in foodstuffs andenables harpagophytum extracts to be purified and titres greater than orequal to 35% to be obtained.

The use of ethyl acetate allows the evaporation—drying operations to becarried out at a much lower temperature than when butanol, for example,is used. This reduction in temperature then enables degradation of theactive ingredients to be limited. Accordingly, ethyl acetate (boilingpoint 77° C. at atmospheric pressure) and water form an azeotrope whichboils at 70.4° C. at atmospheric pressure and at less than 40° C. undera vacuum of 0.1 bar.

In addition, the water-butanol azeotrope contains 42.4% water, while thewater-ethyl acetate azeotrope contains only 8.5% water, which enables itto be recycled industrially for new purifications without additionaltreatment.

The selectivity of ethyl acetate in respect of the desired molecules,iridoid glucosides of harpagophytum, as well as the properties of saidsolvent on evaporation, make it possible to obtain extracts having veryhigh titres (>35%), with a real industrial economic performance, for theproduction of product intended for food supplements.

The equipment used within the context of the step of purification byliquid-liquid extraction is any type which allows two liquids to bemixed, more particularly a stirred reactor or packed column and inparticular of the centrifuge type, which equipment allows the two phasesof the method to be harvested rapidly: the concentrated aqueous phase,depleted of harpagoside, and the organic phase loaded with harpagoside.The method allows more than 90% of the active ingredients present in thestarting aqueous phase to be recovered.

Accordingly, starting from a crude extract in liquid form in aqueousphase, obtained either by crude extraction of the plant with water or bycrude extraction with alcohol followed by removal of the solvent, or byredissolving the crude extract in powder form in water, a method ofpurification by liquid-liquid extraction can be carried out.

The present invention relates also to a method as defined above,characterized in that the crude extract of Harpagophytum procumbens isobtained by a process comprising a step in which a solvent of theaqueous alcoholic type composed of from 0 to 90% alcohol is brought intocontact with dried lateral roots of Harpagophytum procumbens, especiallyby extraction, maceration, decoction or percolation, and a step in whichthe solvent is removed by solid/liquid separation, especially byfiltration, by desolvation or by centrifugation, in order to recoversaid crude extract, and an optional step in which said crude extract isconcentrated in order to obtain said crude extract in the form of athick liquid containing from 2 to 50% dry matter.

The alcohol mentioned above that constitutes the solvent of the aqueousalcoholic type is preferably methanol or ethanol.

The present invention relates also to a method as defined above in whichthe conversion of the concentrated extract in liquid form by physical orphysico-chemical means is carried out by removing the solvent in astream of hot air, by drying, by atomization, by evaporation, bysublimation, by dehydration, or by adsorption on a support.

The present invention relates preferably to a method for preparing aconcentrated extract of Harpagophytum procumbens, in liquid form, havinga harpagoside titre greater than or equal to 5%, preferably from 35 to50%, said method comprising:

-   -   a purification step of the type liquid-liquid extraction between        a crude extract of Harpagophytum procumbens in liquid form in        aqueous phase and an organic solvent selected from the esters,        in order to obtain an aqueous phase and a        harpagoside-concentrated organic phase, and    -   a step in which the solvent is removed from the organic phase        obtained previously in order to obtain said concentrated extract        in liquid form.

The present invention relates preferably to a method for preparing aconcentrated extract of Harpagophytum procumbens, in dry form, having aharpagoside titre greater than or equal to 5%, preferably from 35 to50%, said method comprising:

-   -   a purification step of the type liquid-liquid extraction between        a crude extract of Harpagophytum procumbens in liquid form in        aqueous phase and an organic solvent selected from the esters,        in order to obtain an aqueous phase and a        harpagoside-concentrated organic phase,    -   a step in which the solvent is removed from the organic phase        obtained previously in order to obtain said concentrated extract        in liquid form, and    -   a step in which said concentrated extract in liquid form is        converted by physical or physico-chemical means in order to        obtain a concentrated extract in dry form.

The present invention relates also to extracts as obtained by carryingout the method of the invention as defined above.

The present invention relates to a concentrated extract of Harpagophytumprocumbens, in liquid form, soluble in aqueous phase, having aharpagoside titre greater than or equal to 35%, preferably fromapproximately 35% to approximately 50%, especially from approximately35% to approximately 45% and preferably from approximately 35% toapproximately 40%.

The present invention relates also to a concentrated extract ofHarpagophytum procumbens, in dry form, having a harpagoside titregreater than or equal to 35%, preferably from approximately 35% toapproximately 50%, especially from approximately 35% to approximately45% and preferably from approximately 35% to approximately 40%.

The present invention relates also to a pharmaceutical compositioncomprising as active ingredient a concentrated extract of Harpagophytumprocumbens, in liquid or dry form, in association with apharmaceutically acceptable carrier.

The present invention relates also to a food supplement comprising aconcentrated extract of Harpagophytum procumbens, in liquid or dry form,in association with an acceptable carrier.

EXAMPLES Example 1

1) Preparation of the Crude Extract:

The crude extract is prepared from a tonne of lateral roots ofharpagophytum. The lateral roots are macerated in water, with stirring,for 2 hours. A step of separation between the plant and the solvent bysuccessive filtering operations (600 μm, 100 μm, then 25 μm) is thencarried out. The following step is a step of concentration in vacuo,which allows yet more solvent to be removed and makes it possible toavoid subsequently handling an excessively large amount of solvent.

A crude extract in concentrated form is then obtained.

2) Purification:

The concentrate is extracted directly in liquid phase with 1000 litresof ethyl acetate using a continuous centrifugal extractor.

The organic phase is recovered, and the solvent is removed in vacuo.

A concentrate in aqueous phase is obtained and can be reduced to apowder, for example in a stirred reactor in vacuo.

The resulting product has a harpagoside titre of 35% measured by HPLC.It must be noted that the initial aqueous phase is depleted ofharpagoside and contains less than 0.3% harpagoside.

Example 2

1) Preparation of the Crude Extract:

The crude extract is prepared from 1 kg of lateral roots ofharpagophytum. The lateral roots are macerated in ethanol (70 vol %) at65° C., with stirring, for 2 hours. A step of separation between theplant and the solvent by successive filtering operations (600 μm, 100μm, then 25 μm) is then carried out. The following step is a step ofconcentration in vacuo, which allows yet more solvent to be removed andmakes it possible to avoid subsequently handling an excessively largeamount of solvent.

A crude extract in concentrated form is then obtained (200 ml).

2) Purification:

The concentrate is extracted directly in liquid phase with 1000 ml ofethyl acetate using a continuous centrifugal extractor (at 0° C.).

The organic phase is recovered, and the solvent is removed in vacuo.

A concentrate in aqueous phase is obtained and can be reduced to apowder, for example by lyophilization. Accordingly, within the contextof this example, a powder is obtained (20 g).

The resulting product has a harpagoside titre of 55% measured by HPLC.

1. An extract of Harpagophytum procumbens, in liquid or dry form whereinthe extract has a harpagoside titre from 5% to 50% w/w.
 2. The extractaccording to claim 1, wherein the extract has an iridoid glucoside ofharpagophytum titre of greater than 35%.
 3. The extract as defined inclaim 1 wherein the harpagoside titre is equal to or greater than 35%.4. The extract as defined in claim 1 wherein the extract is obtainedusing an ester organic solvent.
 5. A pharmaceutical compositioncomprising an extract of Harpagophytum procumbens, in liquid or dry formwherein the extract has a harpagoside titre from 5% to 50% w/w.
 6. Thepharmaceutical composition as defined in claim 5, further comprising anacceptable carrier.
 7. A food supplement comprising an extract ofHarpagophytum procumbens, in liquid or dry form wherein the extract hasa harpagoside titre from 5% to 50% w/w.
 8. The food supplement asdefined in claim 7, further comprising an acceptable carrier.